The present invention relates generally to methods and devices for pyrolyzing scrap materials having a high hydrocarbon content and for recovering marketable end products from the pyrolysis of these materials. More specifically, it relates to a system for pyrolyzing scrap rubber shreds and refining the pyrolysis by-products to produce high quality carbon black and plasticizer oil.
Modern society is producing ever increasing amounts of scrap materials having a high hydrocarbon content. Certain scrap material originates from commercial products that have generally been produced through industrial processes requiring hydrocarbon-containing natural resources which may be either renewable (such as forest products) or non-renewable, such as petroleum, oil, and coal. Disposal of such scrap materials presents a problem. They must either be dumped as landfill, put into the ocean, or decomposed/destroyed in some manner. Each of these alternatives presents its own problems; however, the latter solution has the advantage that the end products from such decomposition/destruction may have further commercial value which may justify the cost of the process economically. It is highly desirable to find a way in which to efficiently recover valuable materials from such scrap materials in order to reduce the environmental pollutants which result from their decomposition/destruction.
Scrap material of particular concern is the disposal of automobile tires. In the United States alone approximately 350 million tires are discarded annually. Most of these tires are quartered or shredded and the shreds are sent to land fills after being quartered or shredded. Such shreds constitute about two percent of solid waste in the United States and about 164 million cubic feet per year of land fill space. Moreover, since these shreds are composed of hydrocarbon materials and hydrocarbons are a principle source of energy, the buried tires represent over 90 million MMBTU's per year of wasted energy. An alternate method of disposing of scrap tires is to burn them. This does recover about one-third of the economic value in terms of carbon black and generated energy. However, this method of disposal is not efficient, and it produces environmental pollutants.
Unfortunately, the rubber from scrap tires cannot be recycled directly into the manufacture of new tires because of the different types of rubber involved. A small portion, about 15 percent, of the scrap tire rubber can be recycled as tire chips for use in various end products such as matting and road surface compositions. However, this disposal method is limited in the amount of scrap rubber that can be processed. It is also relatively expensive due to the amount of liquid nitrogen the chip recycling process requires.
Pyrolysis offers great promise for disposal of hydrocarbon-containing scrap materials generally and scrap tires in particular. Pyrolysis provides an efficient, cost effective method for processing large volumes of scrap rubber and recovering marketable end products. Conventional scrap rubber pyrolysis produces two end products. First, it produces a coarse and impure grade of carbon black requiring further processing before it can be reused. The impurities are generally the steel used in the tire carcass, sulfur used in the vulcanization of the rubber, some zinc, and other trace materials. Second, scrap rubber pyrolysis produces a pyrolysis gas having a heavier weight hydrocarbon fraction and a lighter weight hydrocarbon fraction. The heavier weight hydrocarbon fraction, which is condensed as a liquid from the pyrolysis gas, is a low grade oil suitable as fuel oil. The lighter weight hydrocarbon fraction remaining in a vapor state has little value and can typically be recycled back through the pyrolysis process as fuel for the burners; it can also be sold as fuel under certain special circumstances or simply flared to the atmosphere.
Pyrolysis of tire shreds presents several unique problems. First, the pyrolysis gas exiting from the pyrolysis system contains entrained carbon black particles which are difficult to remove during the condensation of the pyrolysis gas into its liquid and vapor fractions. Second, it is difficult to obtain a consistent hydrocarbon condensate composition when condensing the pyrolysis gas into its liquid and vapor fractions. Third, because carbon black has a high affinity for gasses, it frequently contains an excess of pyrolysis gas which is adsorbed while it is still in the pyrolysis system; this presents problems in the further refinement of the carbon black.
It can be seen that a generic model for a Hydrocarbon Recovery System can be considered as being composed of the following three subsystems: a Pyrolysis System, a Gas Processing System, and a Solids Processing System. The Pyrolysis System receives the hydrocarbon-containing material and breaks down the material into a hydrocarbon-containing pyrolysis gas and a solid by using of intense heat in the absence of oxygen. The system may include a input component for handling the input material and delivering it to the pyrolysis process components; it may also include a removal component for providing the pyrolysis gas and solids in a pre-processed form to other systems for further refinement. The Gas Processing System refines the liquid fraction of the pyrolysis gas to produce usable end products. The Solids Processing System refines the impure carbon black provided by the Pyrolysis System to produce a usable form of carbon black, depending upon the application. According to this model, it should be noted that the division of functions between the Gas/Solids Processing Systems and the Pyrolysis System removal component is highly dependent as a practical matter upon the allocation of functions between these two areas. This functional allocation can also depend upon the physical configuration of the components and how they are laid out within the facility.
The Hydrocarbon Recovery System can be generally characterized as a continuous system where the input materials are provided in a more or less continuous rate, rather than in batches, and the products are produced at a continuous rate. It is intended to process feed stocks composed of fairly homogeneous hydrocarbon materials, generally described as waste or scrap products. These feed stocks take the form of scrap rubber produced from used automobile tires which have been shredded; coal or shale having a high sulfur content coal and shale; or forest products such as tree bark, waste lumber, leaves, branches, etc. Ideally, the Hydrocarbon Recovery System will process such materials in an energy efficient, cost effective manner which is environmentally safe with regards to the marketable materials produced and the byproducts of the process, e.g. exhaust gases, pyrolysis vapor, heated coolants, removed contaminants, etc. Such a system will provide end products which are marketable, recoverable, and economical.